Prostate-specific immune responses have been implicated in the pathogenesis of benign prostatic diseases and may be exploited in developing prostate cancer immunotherapy. A pivotal barrier to prostate cancer immunotherapy, however, is tolerance to prostatic or tumor-associated antigens (TAA). T cell tolerance to prostatic TAA can be accomplished via thymic clonal deletion, or via peripheral mechanisms. In our preliminary transgenic mouse studies, prostate TAA-specific T cells were isolated which evaded thymic deletion in young mice, implicating a peripheral tolerance mechanism. Recognizing that peripheral deletion of autoreactive T cells can be mediated by Fas/Fas-Ligand interaction, we hypothesized that disrupting the Fas/Fas-L pathway could facilitate tolerance disruption in TRAMP prostate cancer transgenic mice. To accomplish this experiment in vivo, we used lpr/lpr mice, which lack functional Fas. Hybrid mice were derived carrying the TRAMP genotype (hemizygous for prostate-specific Tag) in a homozygous lpr/lpr background. Immunization of cancer-bearing adult hybrid TRAMP x lpr/lpr mice elicited a potent, Tag-specific CTL response, thereby circumventing prostate cancer antigen - specific tolerance. Based on these preliminary data, we propose studies to address the hypothesis that Fas-mediated T cell apoptosis mediates prostate-specific T cell tolerance. Experiments toward the following three Specific Aims are planned to address this hypothesis: 1. To determine whether interruption of Fas-mediated T cell death will affect innate immunosurveillance against prostatic tumors. 2. To characterize mechanisms responsible for Fas-mediated elimination of T cells that are autoreactive against prostatic Tag tolerogen. 3. To evaluate the role of Fas-mediated T cell elimination in the efficacy of passive (adoptive transfer) and active (immunization) TRAMP prostate cancer immunotherapy. Findings from these studies will elucidate mechanisms of prostate-specific T cell tolerance, that may relate to prostatic diseases in general, and will provide insight regarding possible utility of targeting Fas-mediated T cell death to augment prostate cancer-specific immune responses.These studies will provide basis for preclinical characterization of prostate antigen -specific T cell tolerance and immunity induction in vivo, that will serve to guide future clinical translation of the strategy of disrupting Fas-FasL interaction as a route for circumventing prostate-specific tolerance.